Windshield wiper blades are used to wipe away snow, sleet, rain, water or condensed moisture along with oil, insects, tree sap, dirt and other foreign matter from a vehicle windshield. The blades should have a long useful life to avoid frequent replacement. However, it is well recognized that worn wiper blades develop a tendency to streak or smear and to wear out in the sense that longitudinal portions of the length of the blades cease to perform a useful cleaning action after a relatively short period of use. These disadvantages are difficult to eliminate because of a large number of variables, such as chemical resistance to ozone and sunlight, tear resistance, flexibility, tensile strength, hardness, rigidity and abrasiveness of the blade and uniformity of wiping pressure and contact with the windshield along the length of the blade.
Many attempts have been made to improve wiper blade performance as by providing special contours in the cross-section of the blade, especially the wiping rib or ribs by selection of a blade material, by chemical treatment of the blade and by varying the design of the blade holder. Nevertheless, the problem of streaking or smearing persists.
One prior art wiping blade comprises a number of strips of rubber of varying heights which are assembled with a crimped spine. The strips are of rubber. Each rib includes a 90 degree cut edge of which more than one is in contact with the surface at all times. One problem with the use of such a construction is manufacturing cost.
The U.S. Pat. No. to Fritz, Jr. 4,473,919 discloses a windshield wiper blade comprising a tubular body portion made up of two semicircular sections of different diameter connected by radially extending shoulders. Five ribs project from the small diameter section generally radially with respect to the longitudinal axis of the body. The middle rib of the five constitutes a squeegee rib and is longer radially than the two scraping ribs. Diametrically opposite the squeegee rib is a T-shaped mounting rib which serves the dual purpose of providing a means by which the blade is attached to the windshield wiper mechanism and also functions as a hinge which allows the blade to rotate at the reversal point of each wiping stroke so as to engage the scraping ribs on opposite sides of the squeegee rib with the windshield.
Other prior art patents which disclose wiper blades generally of the type to which this invention relates are U.S. Pat. Nos. 3,881,212, 3,636,583, 2,798,242, 2,589,339, 2,543,383, 2,295,011, 2,006,322, 3,417,421, 1,816,370, 3,428,997 and 3,566,432.
The single greatest factor in wiping efficiency and service life seems to be the maintenance of a sharp wiping contact edge. Once this edge starts to lose its sharpness, the wiping action deteriorates rapidly.